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Summary ISA Arborists’ Certification Study Guide, 4th Edition Study Notes

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Course
ISA Certified Arborist

Institution
ISA Certified Arborist

Study notes taken on each chapter of the Arborists’ Certification Study Guide (4th Edition) that is used to take the ISA Certified Arborist exam. Also includes notes on ANSI Z133. 83 pages of notes.

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Chapter 1 Tree Biology
Wednesday, February 21, 2024 3:37 PM

Introduction

• Tree: woody perennial plant with single or multiple trunks
• Must learn how trees grow to manage them
• Anatomy/morphology - structure/form of a tree
• Physiology – biological, physical, chemical processes within the structure

Tree Anatomy

Basic structure: cells and tissues

• Meristems: tissue where the division of cells occurs, these cells undergo differentiation where
they develop into other tissues/organs that perform different functions – leaves, stems, roots,
flowers, cone, fruit
• Tree growth occurs in two ways
o Primary growth: from the root and shoot tips (height/length) - the apical
meristems
o Secondary growth: in the thickness of stems, branches, roots – the lateral
meristems
• Apical meristems are found inside buds
o Buds have overlapping scales/leaves that protect it and the developing shoot
(some species/tropical trees have naked buds however)
o It's protected by a root cap in the root tips
• Lateral meristems (2 kinds)
o Vascular cambium layer – thin sheath of dividing cells under the bark becoming
the vascular system of the tree and produces 2 kinds of tissues on each side of it
▪ Xylem: on the inside
▪ Phloem: on the outside
o Cork cambium layer – produces outer tissues (periderm), ultimately the bark
(palms lack secondary growth/bark)
• Cellulose – main substance of cell wall
• Lignin – more rigid substance in the cell walls (matrix of long chains of cellulose) that provides
strength for trees to grow tall

Xylem and Phloem
• Xylem - sapwood
• Secondary xylem: xylem produced during secondary growth aka wood with 4 primary
functions
o Conducts water and minerals (collectively sap)
o Mechanical support
o Storage of carbohydrates
o Defence against spread of dysfunction, disease, decay
• Comprised of both dead and living cells
• Cell walls of dead cells comprised of cellulose, lignin and hemicellulose – together they provide
strength that characterizes wood
• Gymnosperms (pines, spruces, etc.) composed of tracheids (conduct water) and parenchyma
cells (store carbs, defend decay – more abundant in angiosperms)
• Xylem vessels are the primary conducting elements in angiosperms – stacks of dead, open-
ended, hollow cells (like straws) and more efficient than tracheids
• The size and distribution of cell types in the xylem determine a lot of the physical and
biological properties of different trees
Ring porous – trees that form wide vessels early in growing season and narrower

ISA Study Guide Notes Page 1

, o Ring porous – trees that form wide vessels early in growing season and narrower
ones later (elm, oak, ash, etc.)
o Diffuse porous – trees that form vessels of uniform size throughout the season
(maple, planetree, linden, etc.)
• Growth rings of a cut tree show the seasonal xylem production, cells smaller as season
progresses
o Earlywood – cells produced early in the season
o Latewood – cells produced later in the season
o Contrast shows the diameter increase in a year
• Exceptions: conifers don't have vessels and palms constantly grow
• Sapwood – xylem that conducts water, and as they age the deeper layers turn into heartwood
• Heartwood – nonconducting, no living cells/biological function, contributes to mechanical
support of tree, resists microorganism invasion, stores carbon (no longer a physiological role
for the tree)
• Pith - central core of tree

• Phloem - inner bark
• Moves photosynthates such as carbohydrates (sugars) produced in the leaves throughout the
tree for storage or consumption
• Phloem transport requires energy while xylem does not (passive)
• Downward movement

• Rays – parenchyma cells that grow radially, extend across the xylem and phloem, transporting
carbs in and out of the sapwood, storing carbs, and restricting wood decay
• Bark – protective layer of the tree, covers branches, stems, sometimes roots, moderates
temperature, defends against injury, reduces water loss
o Lenticels – small openings in the bark, permitting gas exchange of oxygen and
carbon dioxide

Stems
• Apical/terminal buds – buds at the end of a shoot (most active typically)
• Axillary buds – buds along the stem (often dormant, the apical dominance of the terminal bud
prohibits growth sometimes) - they become more active when the shoot lengthens and ages
leading to new shoot development
• Adventitious buds – along the tree (ex: roots) where meristem tissue does not exist, could be
stimulated by loss of apical buds
o Some species (ex: trembling aspen) grow from these buds on the roots – many
trees with a common root system
• Latent buds – dormant under bark until growth is triggered by light or injury
o Epicormic shoots – the growth that occurs from latent buds
• Node – enlarged portion of the twig where leaves and buds develop
o Internode – part of stem between nodes, shows leaf scars and terminal bud scale
scars (scars from when they fall off) - used to measure twig growth
• Lenticels – pores for gas exchange along stem

• Branches – produce and store carbohydrates (sustain themselves, but long distance transport
from trunk/roots occurs too)
o Branch collar – the "shoulder"/swollen area of tissue between the branch and
trunk at the base – this branch union allows for the growth of specialized wood –
dense
o Branch bark ridge – raised area of bark where the branch attaches to the trunk
o Included bark – a defect that develops when the branch and trunk (or two
branches) grow closely together and the bark embeds itself weakening the
junction

Leaves

ISA Study Guide Notes Page 2

,Leaves
• produce food for the tree
o Chlorophyll – green leaf pigment that absorbs sunlight in the chloroplasts (cells)
o Photosynthesis – converts this energy into carbohydrates
o Transpiration – loss of water vapour through leaves (leaf cools)
o Cuticle – protective waxy outer surface of the leaf
o Stomata – small pores on underside of leaf that control loss of water and
exchange of gases
o Guard cells – regulate the opening and closing of the stomata for water/carbon
dioxide movement (respond to light, temperature, humidity)
o Veins – contain phloem and xylem tissues, transport water, elements, and
carbohydrates
o Deciduous – trees that shed their leaves periodically/yearly - due to environmental
changes
o Abscission zone – cell layer formed at the base of the petiole that allows for leaf
drop and then protects the area
o Evergreen – trees that hold their leaves for more than one year
o Fall colours – weather enhances sugars (stored for spring) and triggers breakdown
of chlorophyll allowing other pigments to show – these colours protect from
ultraviolet radiation
▪ Anthocyanins (reds/purples)
▪ Carotenoids (yellows/oranges/reds)

Roots
• Serve 4 primary functions – anchorage, storage, absorption, conduction
o Absorbing roots – small, fibrous tissues at ends of woody roots, hairs that aid in
uptake of water and minerals (like shoot tips they have meristematic zone at the
tip for growth), upper 30cm/12 in of soil
o Lateral roots – near soil surface
o Sinker roots – grow vertically down off lateral roots to anchor and access deeper
water
o Taproot – large, central dominant root in young trees, gets outgrown by other
roots or stopped due to compaction in mature trees
o Root crown/trunk flare – area where roots join the main stem
o Extent and direction of root growth dependent on the soil environment
o Mycorrhizae – the symbiotic relationship between roots and fungi, tree and fungi
benefit one another in nourishment, water/mineral absorption

Tree Physiology

Photosynthesis
• Process by which plants use light energy to build carbon molecules that make carbohydrates
• Takes place in cells that contain chloroplasts
• Chloroplasts contain molecules of chlorophyll - the light-absorbing pigment giving plants green
colour
• Two components involved: carbon dioxide and oxygen
○ Carbon dioxide absorbed from atmosphere through stomata
○ Light energy contained in the chloroplasts are converted to chemical energy
(carbohydrates) and used for growth or stored as starch for later use
○ Oxygen is a by-product released through the stomata
• Photosynthates
○ sugar products resulting from photosynthesis that combined with other elements
produce important compounds
○ Stored as starch for later use if not needed immediately

Respiration

ISA Study Guide Notes Page 3

, Respiration
• Process where carbohydrates are converted into energy
• Independent of light, continues at night
• Important that photosynthesis (energy production) exceeds respiration (energy use)
• It's why it is important that trees must have stored carbohydrates
• Ex: tree defoliated by pests, no foliage, photosynthesis stops/reduced, can used stored starch
to survive

Transpiration
• Loss of water from leaf surfaces in the form of water vapour
• Cools leaves, helps moves water up through the xylem
• Waxy surface of leaves helps prevent uncontrolled water loss
• Gas exchange in stomata - water vapour and oxygen released, carbon dioxide absorbed
○ Each stomatal pore has two guard cells that regulate opening and is influenced by light
(open when light), temperature, cell turgor (the pressure of water inside guard cells),
humidity
○ Transpiration also affected by cuticle thickness, hairs on leaf surface, and
number/location of stomata (ex: thick cuticle, small/hairy leaves - adapted to hot/dry
conditions)

Absorption, Translocation and the Vascular System
• Water is essential to all living cells - used in photosynthesis, maintains cell firmness/fullness,
transports essential elements, roots absorb it and it is used for growth/metabolism, but most
lost through transpiration
• Xylem - series of continuous, tiny conduits for water from roots to tips of shoots, where
evaporation of water from leaves pulls water up through the trees from the roots
• Osmosis - process of water entering young/mycorrhizal roots from region of high water
potential to regional of low water potential
○ Pure water has highest potential (minerals/sugars lowers it)
○ Water moves into roots where the water potential is lower than the soil - but water will
move from roots to soil if opposite (ex: salt concentrations high in soil)
• Food products/carbohydrates/photosynthates are moved through the phloem (requires
energy)
○ "source and sink" - source being the leaves (high carbohydrate concentration) and
moved to the sinks being parts that use more energy than they produce (ex: young
leaves)
○ Does not move all to roots as most think - either utilized or stored in proximity to where
it was produced
• Longitudinal/axial transport: movement of water in the xylem, and photosynthates in the
phloem
• Radial transport: movement of water/nutrients within the tree between cells of different
ages - primarily through ray cells (move things laterally)

Control of Growth and Development
• A tree grows based on its genetic potential and its environmental conditions
○ Ex: a species can have a huge growth potential but is limited by the urban environment
• Light, temperature, gravity are all important to survival
○ Ex: long period of cold exposure may be necessary for budbreak, flowering, seed
germination
• Plant growth regulators/hormones
○ Chemical messengers that control part of the coordination of these processes
○ Processes include cell division, cell elongation, flowering, fruit ripening, leaf drop,
dormancy, root development
○ Major hormone groups include auxins, gibberelins, cytokinins, ethylene, abscisic acid
o Auxins: regulates every aspect of plant growth and development, primarily is in
shoot tips but also important to root development (ex: shoots tips get cut, root
growth inhibited and lateral shoots triggered - do not heavy crown prune to

ISA Study Guide Notes Page 4

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